<template>
  <div class="pagination">

    <!--  上  -->
    <button :disabled="pageNo ===1" @click="$emit('getPageNo', pageNo -1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1"
            @click="$emit('getPageNo', 1)"
            :class="{active: pageNo ===1}"
    >
      1
    </button>

    <button v-if="startNumAndEndNum.start >2">···</button>

    <!-- 中间部分-->
    <button v-for="(page, index) in startNumAndEndNum.end"
            :key="index"
            v-if=" page >= startNumAndEndNum.start"
            @click="$emit('getPageNo', page)"
            :class="{active: pageNo === page}"
    >
      {{page}}
    </button>

    <!--  下  -->
    <button v-if="startNumAndEndNum.end < totalPage - 1 ">···</button>
    <button v-if="startNumAndEndNum.end < totalPage"
            @click="$emit('getPageNo', totalPage)"
            :class="{active: pageNo === totalPage}"
    >
      {{totalPage}}
    </button>
    <button :disabled="pageNo === totalPage" @click="$emit('getPageNo', pageNo + 1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>

  </div>
</template>

<script>
  export default {
    name: "Pagination",
    /*<!-- pageNo:当前页  pageSize：每页展示几条数据
        total:总共的数据  continues：连续展示的页数  -->*/
    props: ['pageNo', 'pageSize', 'total', 'continues'],
    computed: {
      //总共多少页
      totalPage() {
        //向上取整
        return Math.ceil(this.total / this.pageSize)
      },
      //计算出连续的页码的起始的数字和结束的数字
      startNumAndEndNum() {
        const {continues, pageNo, totalPage} = this;
        //先定义两个变量 定义起始的数字 和结束的数字
        let start = 0, end = 0;
        //连续的页码是5 【就是至少5页】 如果出现不正常现象 【就是不够5页】
        //不正常现象 【总页数没有连续的页码多】
        if (continues > totalPage) {
          start = 1;
          end = totalPage
        } else {
          //正常现象 【连续页码是5  总页码是一定大于5的】

          start = pageNo - (continues - 1) / 2;
          end = pageNo + (continues - 1) / 2;
          //向下取整
        /*  start = pageNo - parseInt(continues / 2);
          end = pageNo + parseInt(continues / 2);*/

          //把出现不正常的现象 【start 数字出现 0|负数】 纠正
          if (start < 1) {
            start = 1;
            end = continues;
          }
          //把出现不正常的现象 【end 数字出现大于总页码】 纠正
          if (end > totalPage) {
            start = totalPage - continues + 1;
            end = totalPage
          }
        }
        return {start, end};

      }
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;

    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }

  .active {
    background: skyblue;
  }
</style>